The most common error in geographic code is not in any formula but in the order of two numbers. Most people and most mapping sites write latitude first; GeoJSON, many GIS tools and a lot of APIs write longitude first. Swap them and a point in Madrid lands in the Indian Ocean off the coast of Kenya, and nothing complains. Every endpoint here takes latitude first, and a pair whose first number cannot be a latitude is refused with a hint about the order rather than silently accepted.
The second choice is the shape of the Earth. The haversine formula treats the Earth as a sphere and is off by up to about half a percent, which is several kilometres on an intercontinental distance and enough to matter for aviation, surveying or any comparison with published figures. Distances, bearings and destinations here are solved on the WGS84 ellipsoid with Karney's method, and the spherical estimate is shown alongside for comparison.
Format conversions have quieter traps. A value in degrees, minutes and seconds carries its hemisphere as a letter, and careless parsing loses the sign, putting a western longitude in the east. A geohash identifies a cell, not a point, so the cell size belongs with it. UTM and MGRS divide the globe into zones with exceptions around Norway and Svalbard, and the same place near a zone boundary can be written in two valid ways.
Nothing is geocoded: place names are not turned into coordinates, or coordinates into addresses.
/geo/distance?from=&to=&[unit=]
Distance between two points on the WGS84 ellipsoid (Karney), plus spherical estimate
from: latitude,longitude; to: latitude,longitude; unit (optional): m, km, mi, nmi or ft
curl "https://agent-helper.org/geo/distance?from=55.7558,37.6173&to=40.7128,-74.0060"/geo/bearing?from=&to=
Initial and final bearing (azimuth) from one point to another
from: latitude,longitude; to: latitude,longitude
curl "https://agent-helper.org/geo/bearing?from=51.5074,-0.1278&to=48.8566,2.3522"/geo/destination?from=&bearing=&distance=&[unit=]
Point reached from a start point, bearing and distance (direct geodesic problem)
from: latitude,longitude; bearing: degrees clockwise from true north; distance: distance; unit (optional): m, km, mi, nmi or ft
curl "https://agent-helper.org/geo/destination?from=55.7558,37.6173&bearing=90&distance=100"/geo/midpoint?from=&to=
Midpoint of the geodesic between two points
from: latitude,longitude; to: latitude,longitude
curl "https://agent-helper.org/geo/midpoint?from=55.7558,37.6173&to=59.9343,30.3351"/geo/dms?point=
Decimal degrees to degrees, minutes, seconds
point: latitude,longitude in decimal degrees
curl "https://agent-helper.org/geo/dms?point=55.7558,37.6173"/geo/decimal?lat=&lon=
Degrees-minutes-seconds text to decimal degrees
lat: latitude, e.g. 55°45'20.9"N; lon: longitude, e.g. 37°37'02.3"E
curl "https://agent-helper.org/geo/decimal?lat=55%C2%B045'20.9%22N&lon=37%C2%B037'02.3%22E"/geo/geohash?point=&[precision=]
Encode a point as a geohash
point: latitude,longitude; precision (optional): characters, 1-12
curl "https://agent-helper.org/geo/geohash?point=57.64911,10.40744&precision=11"/geo/geohash/{hash}
Decode a geohash to its cell centre and size
hash: geohash
curl "https://agent-helper.org/geo/geohash/u4pruydqqvj"/geo/utm?point=
Latitude/longitude to UTM zone, easting, northing (WGS84)
point: latitude,longitude
curl "https://agent-helper.org/geo/utm?point=55.7558,37.6173"/geo/mgrs?point=&[precision=]
Latitude/longitude to an MGRS grid reference
point: latitude,longitude; precision (optional): digits per axis 0-5 (5 = 1 m)
curl "https://agent-helper.org/geo/mgrs?point=55.7558,37.6173"/geo/mgrs/{code}
MGRS grid reference to latitude/longitude (south-west corner of the square)
code: MGRS reference
curl "https://agent-helper.org/geo/mgrs/37UDB1322479766"